Alternating copolymers of phenylene vinylene and biarylene vinylene, preparation method thereof, and organic thin flim transister comprising the same

ABSTRACT

Disclosed herein are an alternating copolymer of phenylene vinylene and biarylene vinylene, a preparation method thereof, and an organic thin film transistor including the same. The organic thin film transistor maintains low off-state leakage current and realizes a high on/off current ratio and high charge mobility because the organic active layer thereof is formed of an alternating copolymer of phenylene vinylene and biarylene vinylene.

PRIORITY STATEMENT

This non-provisional application claims priority under U.S.C. § 119 toKorean Patent Application No. 10-2007-0113754, filed on Nov. 8, 2007, inthe Korean Intellectual Property Office (KIPO), the entire contents ofwhich are incorporated herein by reference.

BACKGROUND

1. Field of the Invention

This disclosure is directed to an alternating copolymer of phenylenevinylene and biarylene vinylene, a preparation method thereof, and anorganic thin film transistor comprising the same, and, moreparticularly, to an alternating copolymer of phenylene vinylene andbiarylene vinylene, which comprises phenylene vinylene and biarylenevinylene alternating in the polymer backbone, and thus, when applied tothe organic active layer of an organic thin film transistor, a highon/off current ratio and high charge mobility can be imparted while lowoff-state leakage current is maintained, and to a preparation methodthereof and an organic thin film transistor comprising the same.

2. Description of the Related Art

Generally, an organic thin film transistor (OTFT) comprises a substrate,a gate electrode, an insulating layer, source/drain electrodes, and achannel layer, and is classified into a bottom contact (BC) type, inwhich a channel layer is formed on source/drain electrodes, and a topcontact (TC) type, in which metal electrodes are formed on a channellayer through mask deposition.

The channel layer of the TFT is typically formed of an inorganicsemiconductor material, such as silicon (Si). Recently, however, inorder to realize large, inexpensive, and flexible displays, the demandto use an organic semiconductor material, in place of expensiveinorganic material, requiring a high-temperature vacuum process, isincreasing.

Thus, thorough research into organic semiconductor materials useful asthe channel layer of OTFTs and transistor properties using the same isbeing conducted. Examples of low-molecular-weight or oligomeric organicsemiconductor materials include merocyanine, phthalocyanine, perylene,pentacene, C60, or thiophene oligomer. Lucent Technologies and 3Mreported the use of pentacene monocrystals to realize OTFTs having highcharge mobility of 3.2˜5.0 cm²/Vs (Mat. Res. Soc. Symp. Proc. 2003, Vol.771, L6.5.1˜L6.5.11).

In addition, OTFTs using a thiophene polymer as the polymer materialhave been reported. Although these OTFTs have properties inferior tothose of OTFTs using low-molecular-weight material, they areadvantageous with respect to the processability thereof because a largearea may be realized at a low expense through a solution process, forexample, a printing process. Further, the organic semiconductor polymermaterial has lower charge mobility than low-molecular-weight material,including pentacene, but is preferable thereto because it eliminates theneed for a high operating frequency and enables the inexpensivefabrication of TFTs.

With the goal of commercializing the OTFTs, off-state leakage current,in addition to charge mobility, must be minimized. That is, a highon/off current ratio should be satisfied. To this end, various attemptsto improve such properties are being made.

SUMMARY

Disclosed herein is a novel alternating copolymer of phenylene vinyleneand biarylene vinylene, which has high solubility in an organic solventand high processability and exhibits partial coplanarity to thus realizeamorphous properties and superior π-stacking properties when formed intoa film, and a method of preparing the same.

Also disclosed herein is an OTFT, the organic active layer of which isformed of an alternating copolymer of phenylene vinylene and biarylenevinylene prepared by adding an arylene group to an arylene derivativeand having a decreased band gap, thus realizing high mobility of chargesand holes.

Also disclosed herein is an electronic device, comprising thealternating copolymer of phenylene vinylene and biarylene vinylene.

In one embodiment, a novel alternating copolymer of phenylene vinyleneand biarylene vinylene is provided, which is adapted for use in theorganic active layer of an OTFT to improve device properties. Such analternating copolymer of phenylene vinylene and biarylene vinylene maybe represented by Formula 1 below:

wherein R¹, R², R³, and R⁴ are each independently selected from thegroup consisting of hydrogen, a hydroxyl group, a C_(1˜20) linear,branched or cyclic alkyl group, a C_(1˜20) alkoxyalkyl group, and aC_(1˜16) linear, branched or cyclic alkoxy group, X is selected from thegroup consisting of S, O, NH, N-methyl, and Se, and n is an integer from4 to 200.

The alternating copolymer of phenylene vinylene and biarylene vinyleneis a novel p-type polymer organic semiconductor, having a structure inwhich phenylene vinylene and biarylene vinylene having an aryl groupacting as a hole donor alternate in the polymer backbone, and exhibitingconductive polymer properties.

In another embodiment, a method of preparing the alternating copolymerof phenylene vinylene and biarylene vinylene is provided. The method mayinclude copolymerizing a monomer represented by Formula 4 below with amonomer represented by Formula 5 below:

wherein R¹ and R² are each independently selected from the groupconsisting of hydrogen, a hydroxyl group, a C_(1˜20) linear, branched orcyclic alkyl group, a C_(1˜20) alkoxyalkyl group, and a C_(1˜16) linear,branched or cyclic alkoxy group, and Y is a C_(1˜4) alkyl group; and

wherein R³ and R⁴ are each independently selected from the groupconsisting of hydrogen, a hydroxyl group, a C_(1˜20) linear, branched orcyclic alkyl group, a C_(1˜20) alkoxyalkyl group, and a C_(1˜16) linear,branched or cyclic alkoxy group, and X is selected from the groupconsisting of S, O, NH, N-methyl, and Se.

In a further embodiment, an OTFT is provided, which comprises asubstrate, a gate electrode, a gate insulating layer, an organic activelayer, and source/drain electrodes, the organic active layer beingformed of the alternating copolymer of phenylene vinylene and biarylenevinylene. Because the organic active layer of the OTFT is formed of thealternating copolymer of phenylene vinylene and biarylene vinylene, lowoff-state leakage current may be maintained and a high on/off currentratio may be attained. Further, the arylene group is added to thearylene derivative, and thus a band gap may be decreased, and charges orholes may be efficiently transported, resulting in high charge mobility.

The alternating copolymer of phenylene vinylene and biarylene vinylenemay also be applied to various electronic devices, examples of theelectronic device including, but not being limited to, an organic lightemitting device (OLED), an organic photovoltaic device, or a sensor.

BRIEF DESCRIPTION OF THE DRAWINGS

Example embodiments will be more clearly understood from the followingdetailed description taken in conjunction with the accompanyingdrawings, in which:

FIG. 1 is an exemplary schematic cross-sectional view illustrating anOTFT;

FIG. 2 is a ¹H-NMR spectrum of an alternating copolymer (PPVBTV-1) of aphenylene vinylene (PV) derivative and a bithiophene vinylene (BTV)derivative, obtained in Preparative Example 1;

FIG. 3 is a UV-VIS spectrum of a film of an alternating copolymer(PPVBTV-3) of a phenylene vinylene (PV) derivative and a bithiophenevinylene (BTV) derivative, obtained in Preparative Example 3;

FIG. 4 is a current transfer curve of the alternating copolymer(PPVBTV-3) of a phenylene vinylene (PV) derivative and a bithiophenevinylene (BTV) derivative, obtained in Preparative Example 3; and

FIG. 5 is a current transfer curve of the alternating copolymer(PPVBTV-7) of a phenylene vinylene (PV) derivative and a bithiophenevinylene (BTV) derivative, obtained in Preparative Example 7.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

Hereinafter, example embodiments will be described in detail withreference to the attached drawings. Example embodiments may, however, beembodied in many different forms and should not be construed as beinglimited to the embodiments set force herein. Rather, these embodimentsare provided so that this disclosure will be thorough and complete, andwill fully convey the scope of example embodiments to those skilled inthe art.

In accordance with one embodiment, an alternating copolymer of phenylenevinylene and biarylene vinylene may be represented by Formula 1 below:

wherein R¹, R², R³, and R⁴ are each independently selected from thegroup consisting of hydrogen, a hydroxyl group, a C_(1˜20) linear,branched or cyclic alkyl group, a C_(1˜20) alkoxyalkyl group, and aC_(1˜16) linear, branched or cyclic alkoxy group, X is selected from thegroup consisting of S, O, NH, N-methyl, and Se, and n is an integer from4 to 200.

In addition, examples of the alternating copolymer of phenylene vinyleneand biarylene vinylene include, but are not limited to, a compoundselected from the group represented by Formula 2 below:

wherein R¹ and R² are each independently selected from the groupconsisting of a hexyl group, a heptyl group, and an octyl group, R³ isselected from the group consisting of a butyl group, a hexyl group, andan octyl group, and n is an integer from 4 to 200.

In addition, examples of the alternating copolymer of phenylene vinyleneand biarylene vinylene include, but are not limited to, a compoundselected from the group represented by Formula 3 below.

The alternating copolymer of phenylene vinylene and biarylene vinylenehas high solubility in an organic solvent and high processability, andexhibits partial coplanarity.

Further, when the compound, in which phenylene vinylene and biarylenevinylene alternate in the polymer backbone, is formed into a film,amorphous properties and superior π-stacking properties may bemanifested.

In accordance with another embodiment, a method of preparing thealternating copolymer of phenylene vinylene and biarylene vinylene isprovided. The method of preparing the alternating copolymer of phenylenevinylene and biarylene vinylene includes copolymerizing a monomerrepresented by Formula 4 below with a monomer represented by Formula 5below:

wherein R¹ and R² are each independently selected from the groupconsisting of hydrogen, a hydroxyl group, a C_(1˜20) linear, branched orcyclic alkyl group, a C_(1˜20) alkoxyalkyl group, and a C_(1˜16) linear,branched or cyclic alkoxy group, and

Y is a C_(1˜4) alkyl group; and

wherein R³ and R⁴ are each independently selected from the groupconsisting of hydrogen, a hydroxyl group, a C_(1˜20) linear, branched orcyclic alkyl group, a C_(1˜20) alkoxyalkyl group, and a C_(1˜16) linear,branched or cyclic alkoxy group, and

X is selected from the group consisting of S, O, NH, N-methyl, and Se.

Examples of the monomer represented by Formula 5, include, but are notlimited to, a monomer selected from the group represented by Formula 6below:

wherein R³ and R⁴ are each independently selected from the groupconsisting of hydrogen, a hydroxyl group, a C_(1˜20) linear, branched orcyclic alkyl group, a C_(1˜20) alkoxyalkyl group, and a C_(1˜16) linear,branched or cyclic alkoxy group.

Further, examples of the monomer represented by Formula 5, include, butare not limited to, a monomer selected from the group represented byFormula 7 below.

According to the example embodiments, the alternating copolymer ofphenylene vinylene and biarylene vinylene may be polymerized through aHorner-Emmons reaction. Through such a reaction, dialkyl phosphoric acidis removed from the phenylene derivative, and a double bond is formedbetween the phenylene derivative and the biarylene derivative, thusobtaining an alternating copolymer of phenylene vinylene and biarylenevinylene. In the above reaction, sodium methoxide or potassium butoxidemay be used as a reaction accelerator, and examples of thepolymerization solvent include dimethylformaldehyde (DMF),tetrahydrofuran (THF), or N-methylpyrrolidinone (NMP).

The polymerization reaction of the alternating copolymer of phenylenevinylene and biarylene vinylene is shown by way of example in Scheme 1below.

Here, n is an integer from 4 to 200.

The alternating copolymer (PPVBTV-1) of phenylene vinylene andbithiophene vinylene obtained through Scheme 1 has a number averagemolecular weight ranging from about 10,000 to about 100,000.

According to the example embodiments, the alternating copolymer ofphenylene vinylene and biarylene vinylene preferably has a numberaverage molecular weight of 10,000 or more. When the number averagemolecular weight thereof is less than 10,000, it is difficult to form athin film, and poor current transfer properties result.

In accordance with a further embodiment, an OTFT, comprising asubstrate, a gate electrode, a gate insulating layer, an organic activelayer, and source/drain electrodes, is provided, in which the organicactive layer is formed of the alternating copolymer of phenylenevinylene and biarylene vinylene. In this way, when the organic activelayer of the OTFT is formed of the alternating copolymer of phenylenevinylene and biarylene vinylene, low off-state leakage current ismaintained, and simultaneously, a high on/off current ratio is realized.Further, an arylene group is added to an arylene derivative, thusdecreasing a band gap and efficiently transporting electrons or holes,resulting in high charge mobility.

Specifically, the alternating copolymer of phenylene vinylene andbiarylene vinylene according to the example embodiments may be used as anovel organic semiconductor material to manufacture the active layer ofthe OTFT. Examples of the process of forming the organic active layerinclude, but are not limited to, screen printing, printing, spincoating, dipping, or ink jetting.

FIG. 1 is an exemplary schematic cross-sectional view illustrating theOTFT.

With reference to FIG. 1, the OTFT is manufactured to have a structure,including a substrate 1, a gate electrode 2, a gate insulating layer 3,a source electrode 4, a drain electrode 5, and an organic active layer6, but the example embodiments are not limited thereto.

The gate insulating layer 3 of the OTFT is formed of a typical insulatorhaving a high dielectric constant, and specific examples of theinsulator include, but are not limited to, a ferroelectric insulatorselected from the group consisting of Ba_(0.33)Sr_(0.66)TiO₃ (BST),Al₂O₃, Ta₂O₅, La₂O₅, Y₂O₃ and TiO₂, an inorganic insulator selected fromthe group consisting of PbZr_(0.33)Ti_(0.66)O₃ (PZT), Bi₄Ti₃O₁₂, BaMgF₄,SrBi₂(TaNb)₂O₉, Ba(ZrTi)O₃ (BZT), BaTiO₃, SrTiO₃, Bi₄Ti₃0₁₂, SiO₂,SiN_(x) and AlON, or an organic insulator including polyimide, BCB(benzocyclobutene), parylene, polyacrylate, polyvinylalcohol andpolyvinylphenol.

The gate electrode 2, the source electrode 4, and the drain electrode 5of the OTFT are formed of typical metal, and specific examples of themetal include, but are not limited to, gold (Au), silver (Ag), aluminum(Al), nickel (Ni), or indium tin oxide (ITO).

Examples of material for the substrate of the OTFT include, but are notlimited to, glass, polyethylene naphthalate (PEN), polyethyleneterephthalate (PET), polycarbonate, polyvinylalcohol, polyacrylate,polyimide, polynorbornene, or polyethersulfone (PES).

The alternating copolymer of phenylene vinylene and biarylene vinyleneaccording to the example embodiments may also be applied to variouselectronic devices, in addition to the OTFT. Examples of the electronicdevice include, but are not limited to, an organic light emitting device(OLED), an organic photovoltaic device, or a sensor.

Hereinafter, example embodiments will be described in detail withreference to Examples. These Examples are set forth to illustrateexample embodiments, but should not be construed to be the limit ofexample embodiments.

EXAMPLES Synthesis of Alternating Copolymers of Phenylene Vinylene andBiarylene Vinylene

Alternating copolymers (PPVBTV-1 to PPVBTV-9) of phenylene vinylene andbiarylene vinylene were synthesized through the reaction according toScheme 2 below.

Preparative Example 1 Synthesis of Alternating Copolymer (PPVBTV-1) ofPhenylene Vinylene (PV) Derivative and Bithiophene Vinylene (BTV)Derivative

Into a flask containing 50 ml of anhydrous tetrahydrofuran (THF),tetramethyl-ethylenediamine (16 mmol) and butyl lithium (16 mmol) wereadded, and then stirred for 30 min. Further, the stirred mixture wasadded with 3-octylthiophene (15 mmol), stirred at room temperature for10 min, and then heated under reflux for 2 hours. The reaction mixturewas cooled to room temperature and then to −78° C. using acetone-dryice. The reaction mixture was added with copper chloride (19 mmol) andthen stirred while the temperature thereof was gradually increased toroom temperature. The reaction mixture was filtered with a Celite pad,concentrated, and passed through a silica gel column, thus obtaining acompound 2 separated in the form of a yellow solid (yield: 80%). The ¹HNMR results of the compound 2 were as follows:

¹H NMR (CDCl₃) d 7.0 (s, 2H), 6.8 (s, 2H), 2.6 (t, 4H), 1.7 (m, 4H), 1.3(m, 20H), 0.9 (t, 6H).

The compound 2 (4.9 mmol) was dissolved in 50 ml of anhydrous ether andthen added with butyl lithium (11.2 mmol) in a nitrogen atmosphere. Thereaction mixture was heated under reflux for 2 hours and then cooled toroom temperature. Subsequently, to the reaction mixture,dimethylformamide (10.7 mmol) was added in droplets, followed byconducting stirring for 18 hours. Thereafter, the reaction mixture wasadded with a saturated ammonium chloride aqueous solution, and thenextracted two times with ether. The collected organic layer was driedand concentrated under reduced pressure, thus obtaining a red solid. Thesolid was dissolved in ether and then cooled to −78° C., thus obtainingan organic solid, which was then filtered, thereby obtaining a compound3 (yield: 75%). The ¹H NMR results of the compound 3 were as follows.

¹H NMR (CDCl₃) d 10.0 (s, 2H), 7.2 (s, 2H), 2.9 (t, 4H), 1.7 (m, 4H),1.3 (m, 20H), 0.9 (t, 6H).

In a flask, a phenylene vinylene (PV) derivative (in Formula 4, R¹,R²=—OC₈H₁₇, 1 mmol) and the compound 3 (1 mmol) were dissolved in THF (2ml) and then heated to about 80° C. The reaction mixture was slowlyadded with a solution of t-BuOK (3 mmol) in THF. The reaction wasconducted for 12 hours, after which the reaction product wasre-precipitated in methanol, thus recovering a high-molecular-weightmaterial, which was then dried, thereby obtaining PPVBTV-1 of Formula 3(yield: 45%, Mn=18,000). The ¹H-NMR spectrum of the PPVBTV-1 is shown inFIG. 2.

Preparative Example 2 Synthesis of Alternating Copolymer (PPVBTV-2) ofPhenylene Vinylene (PV) Derivative and Bithiophene Vinylene (BTV)Derivative

An alternating copolymer (PPVBTV-2 of Formula 3) was synthesized in thesame manner as in Preparative Example 1, with the exception that aphenylene vinylene (PV) derivative (in Formula 4, R¹, R²=Heptyl-Oxy) wasused as a monomer. (Yield: 40%, Mn=14,000).

Preparative Example 3 Synthesis of Alternating Copolymer (PPVBTV-3) ofPhenylene Vinylene (PV) Derivative and Bithiophene Vinylene (BTV)Derivative

An alternating copolymer (PPVBTV-3 of Formula 3) was synthesized in thesame manner as in Preparative Example 1, with the exception that aphenylene vinylene (PV) derivative (in Formula 4, R¹, R²=Hexyl-Oxy) wasused as a monomer. (Yield: 40%, Mn=16,000). The UV-VIS spectrum of afilm of the PPVBTV-3 is shown in FIG. 3.

Preparative Example 4 Synthesis of Alternating Copolymer (PPVBTV-4) ofPhenylene Vinylene (PV) Derivative and Bithiophene Vinylene (BTV)Derivative

An alternating copolymer (PPVBTV-4 of Formula 3) was synthesized in thesame manner as in Preparative Example 1, with the exception that3-hexylthiophene was used as a starting material. (Yield: 45%,Mn=16,000).

Preparative Example 5 Synthesis of Alternating Copolymer (PPVBTV-5) ofPhenylene Vinylene (PV) Derivative and Bithiophene Vinylene (BTV)Derivative

An alternating copolymer (PPVBTV-5 of Formula 3) was synthesized in thesame manner as in Preparative Example 2, with the exception that3-hexylthiophene was used as a starting material. (Yield: 40%,Mn=19,000).

Preparative Example 6 Synthesis of Alternating Copolymer (PPVBTV-6) ofPhenylene Vinylene (PV) Derivative and Bithiophene Vinylene (BTV)Derivative

An alternating copolymer (PPVBTV-6 of Formula 3) was synthesized in thesame manner as in Preparative Example 3, with the exception that3-hexylthiophene was used as a starting material. (Yield: 40%,Mn=18,000).

Preparative Example 7 Synthesis of Alternating Copolymer (PPVBTV-7) ofPhenylene Vinylene (PV) Derivative and Bithiophene Vinylene (BTV)Derivative

An alternating copolymer (PPVBTV-7 of Formula 3) was synthesized in thesame manner as in Preparative Example 1, with the exception that3-butylthiophene was used as a starting material. (Yield: 40%,Mn=12,000).

Preparative Example 8 Synthesis of Alternating Copolymer (PPVBTV-8) ofPhenylene Vinylene (PV) Derivative and Bithiophene Vinylene (BTV)Derivative

An alternating copolymer (PPVBTV-8 of Formula 3) was synthesized in thesame manner as in Preparative Example 2, with the exception that3-butylthiophene was used as a starting material. (Yield: 40%,Mn=12,000).

Preparative Example 9 Synthesis of Alternating Copolymer (PPVBTV-9) ofPhenylene Vinylene (PV) Derivative and Bithiophene Vinylene (BTV)Derivative

An alternating copolymer (PPVBTV-9 of Formula 3) was synthesized in thesame manner as in Preparative Example 3, with the exception that3-butylthiophene was used as a starting material. (Yield: 40%,Mn=11,000).

[Fabrication of OTFT] Example 1 Fabrication of OTFT Using PPVBTV-1

On a washed glass substrate, chromium for a gate electrode was depositedto a thickness of 1000 Å through sputtering, after which SiO₂ for a gateinsulating film was deposited to a thickness of 1000 Å through CVD.Subsequently, ITO for source/drain electrodes was deposited thereon to athickness of 1200 Å through sputtering. Before the organic semiconductormaterial was deposited, the substrate was washed with isopropyl alcoholfor 10 min and was then dried. Subsequently, the substrate having ITOdeposited thereon was immersed in a 10 mM octadecyltrichlorosilanesolution in chloroform for 30 sec, washed with acetone, and then dried.Subsequently, the alternating copolymer (PPVBTV-1) of phenylene vinylene(PV) and biarylene vinylene (BTV), synthesized in Preparative Example 1,was dissolved to a concentration of 1 wt % in chloroform, applied on thesubstrate to a thickness of 1000 Å at 1000 rpm, and then baked at 100°C. for 1 hour in an argon atmosphere, thereby fabricating the OTFT.

Examples 2 to 9 Fabrication of OTFTs Using PPVBTVs

OTFTs were fabricated in the same manner as in Example 1, with theexception that the types of alternating copolymer of phenylene vinyleneand biarylene vinylene were changed as shown in Table 1 below.

The properties of the OTFTs were measured. The results are shown inTable 1 below.

[Evaluation of Properties of OTFTs]

The current transfer properties of the OTFTs fabricated in Examples 1 to9 were measured using a semiconductor characterization system(4200-SCS), available from KEITHLEY. The current transfer curve ofPPVBTV-3 is shown in FIG. 4, and the current transfer curve of PPVBTV-7is shown in FIG. 5. Further, the electrical properties based on thecurrent transfer properties were calculated as follows. The results arealso shown in Table 1 below.

TABLE 1 Type of Charge On-Off Current Off-State Leakage PPVBTV Mobility(cm²) Ratio Current (A) Ex. 1 PPVBTV-1 0.001 1000 3 × 10⁻¹¹ Ex. 2PPVBTV-2 0.003 7000 7 × 10⁻¹¹ Ex. 3 PPVBTV-3 0.012 1000 1 × 10⁻¹⁰ Ex. 4PPVBTV-4 0.00002 100 1 × 10⁻¹⁰ Ex. 5 PPVBTV-5 0.00088 1000 1 × 10⁻¹⁰ Ex.6 PPVBTV-6 0.0005 500 1 × 10⁻¹⁰ Ex. 7 PPVBTV-7 0.03 300000 2 × 10⁻¹⁰ Ex.8 PPVBTV-8 0.002 5000 1 × 10⁻¹⁰ Ex. 9 PPVBTV-9 0.001 100 1 × 10⁻¹⁰

The charge mobility was calculated from the following current equationfor the saturation region. That is, the current equation for thesaturation region was converted into a graph relating (I_(SD))^(1/2) andV_(G), and the charge mobility was calculated from the slope of theconverted graph:

$I_{SD} = {\frac{W\; C_{o}}{2L}{\mu \left( {V_{G} - V_{T}} \right)}^{2}}$$\sqrt{I_{SD}} = {\sqrt{\frac{\mu \; C_{o}W}{2L}}\left( {V_{G} - V_{T}} \right)}$${slope} = \sqrt{\frac{\mu \; C_{o}W}{2L}}$$\mu_{FET} = {({slope})^{2}\frac{2L}{C_{o}W}}$

wherein I_(SD) is the source-drain current, μ or μ_(FET) is the chargemobility, C_(o) is the oxide film capacitance, W is the channel width, Lis the channel length, V_(G) is the gate voltage, and V_(T) is thethreshold voltage.

The off-state leakage current (I_(off)), which is the current flowing inthe off-state, was taken from the minimum current in the off-state ofthe on/off current ratio.

The on/off current ratio (I_(on)/I_(off)) was taken from the ratio ofmaximum current in the on-state to minimum current in the off-state.

As is apparent from Table 1, the OTFTs of Examples 1 to 9 using thealternating copolymers of phenylene vinylene and biarylene vinylenecould be seen to realize considerably low off-state leakage current anda high on/off current ratio.

As described hereinbefore, the alternating copolymer of phenylenevinylene and biarylene vinylene according to the example embodiments isa novel p-type polymer organic semiconductor. In the case where such analternating copolymer is used for an organic active layer of an OTFT,the electrical properties of the OTFT can be improved. For example, theOTFT using the alternating copolymer of phenylene vinylene and biarylenevinylene according to the example embodiments can manifest low leakagecurrent, high charge mobility, and superior stability.

Although example embodiments have been disclosed for illustrativepurposes, those skilled in the art will appreciate that variousmodifications, additions and substitutions are possible, withoutdeparting from the scope and spirit of the invention as disclosed in theaccompanying claims.

1. An alternating copolymer of phenylene vinylene and biarylenevinylene, represented by Formula 1 below:

wherein R¹, R², R³, and R⁴ are each independently selected from a groupconsisting of hydrogen, a hydroxyl group, a C_(1˜20) linear, branched orcyclic alkyl group, a C_(1˜20) alkoxyalkyl group, and a C_(1˜16) linear,branched or cyclic alkoxy group, X is selected from a group consistingof S, O, NH, N-methyl, and Se, and n is an integer from 4 to
 200. 2. Thealternating copolymer of claim 1, wherein the alternating copolymer ofphenylene vinylene and biarylene vinylene comprises a compound selectedfrom a compound group represented by Formula 2 below:

wherein R¹ and R² are each independently selected from a groupconsisting of a hexyl group, a heptyl group, and an octyl group, R³ isselected from a group consisting of a butyl group, a hexyl group, and anoctyl group, and n is an integer from 4 to
 200. 3. The alternatingcopolymer of claim 1, wherein the alternating copolymer of phenylenevinylene and biarylene vinylene comprises a compound selected from acompound group represented by Formula 3 below:


4. A method of preparing an alternating copolymer of phenylene vinyleneand biarylene vinylene, comprising copolymerizing a monomer representedby Formula 4 below with a monomer represented by Formula 5 below:

wherein R¹ and R² are each independently selected from a groupconsisting of hydrogen, a hydroxyl group, a C_(1˜20) linear, branched orcyclic alkyl group, a C_(1˜20) alkoxyalkyl group, and a C_(1˜16) linear,branched or cyclic alkoxy group, and Y is a C_(1˜4) alkyl group; and

wherein R³ and R⁴ are each independently selected from a groupconsisting of hydrogen, a hydroxyl group, a C_(1˜20) linear, branched orcyclic alkyl group, a C_(1˜20) alkoxyalkyl group, and a C_(1˜16) linear,branched or cyclic alkoxy group, and X is selected from a groupconsisting of S, O, NH, N-methyl, and Se.
 5. The method of claim 4,wherein the monomer represented by Formula 5 comprises a monomerselected from a monomer group represented by Formula 6 below:

wherein R³ and R⁴ are each independently selected from a groupconsisting of hydrogen, a hydroxyl group, a C_(1˜20) linear, branched orcyclic alkyl group, a C_(1˜20) alkoxyalkyl group, and a C_(1˜16) linear,branched or cyclic alkoxy group.
 6. The method of claim 4, wherein themonomer represented by Formula 5 comprises a monomer selected from amonomer group represented by Formula 7 below:


7. An organic thin film transistor, comprising a substrate, a gateelectrode, a gate insulating layer, an organic active layer, andsource/drain electrodes, in which the organic active layer is formed ofan alternating copolymer of phenylene vinylene and biarylene vinylene,represented by Formula 1 below:

wherein R¹, R², R³, and R⁴ are each independently selected from a groupconsisting of hydrogen, a hydroxyl group, a C_(1˜20) linear, branched orcyclic alkyl group, a C_(1˜20) alkoxyalkyl group, and a C_(1˜16) linear,branched or cyclic alkoxy group, X is selected from a group consistingof S, O, NH, N-methyl, and Se, and n is an integer from 4 to
 200. 8. Theorganic thin film transistor of claim 7, wherein the alternatingcopolymer of phenylene vinylene and biarylene vinylene comprises acompound selected from a compound group represented by Formula 2 below:

wherein R¹ and R² are each independently selected from a groupconsisting of a hexyl group, a heptyl group, and an octyl group, R³ isselected from a group consisting of a butyl group, a hexyl group, and anoctyl group, and n is an integer from 4 to
 200. 9. The organic thin filmtransistor of claim 7, wherein the alternating copolymer of phenylenevinylene and biarylene vinylene comprises a compound selected from acompound group represented by Formula 3 below:


10. An electronic device, comprising the alternating copolymer ofphenylene vinylene and biarylene vinylene of any one of claims 1 to 3.11. The electronic device of claim 10, which is an organic lightemitting device (OLED), an organic photovoltaic device, or a sensor.